Hundreds of Mexican Indians have fled their village in the southern state of Chiapas after surviving a paramilitary attack in which at least 45 people were killed. The survivors say supporters of the ruling Institutional Revolutionary Party opened fire on them during a religious service in the village of Acteal. As Emma Patterson reports from Chiapas, the attack is the worst of its kind since the Zapatista rebels took up arms in 1994, and has led to heightened tension in one of Mexico's poorest and most troubled state:

Survivors of the massacre have described how they ran for their lives as a group of masked gunmen burst into their village. The paramilitaries, they say, opened fire indiscriminately.

Among the victims were at least 15 children. Some were shot, others beaten to death in a round of killing which lasted for more than five hours.

The survivors are now seeking refuge in nearby communities. They say they're too afraid ever to return home.

Witnesses say the gunmen were local members of the ruling Institutional Revolutionary Party. Party leaders have denied any involvement.

But this latest attack is not without precedent.

Pro-government paramilitary organisations have been blamed for a series of attacks during the past few months, most of them directed against the Zapatista rebels and their supporters.

Since taking up arms four years ago, the Zapatistas, along with other indigenous organisations, have challenged the authority of the governing party and the interests of powerful landowners.

Tensions between the two sides have led to open conflict and forced thousands of people to flee their homes.

But this is the worst attack of its kind since the violence began.

Church officials say the simmering conflict is the fault of the government and its reluctance to re-start peace talks with the Zapatistas.

In a televised address to the nation, the Mexican president, Ernesto Zedillo, has promised a full enquiry.

But the massacre at Acteal is part of a wider conflict, which with the passing years has grown ever more complicated and intractable.